Oxalic-acid ester of paracresol and process of making same.



UNITED STATES PATENT OFFICE.

LEOPOLD KAI-IL, OF SCHWIENTOOHLOWITZ, GERMANY, ASSIGNOR TO RUDOLFRUETGERS, OF OHARLOTTENBURG, GERMANY.

OXALIC- ACID ESTER OF PARACRllSOL AND PROCESS OF MAKING SAME.

SPECIFICATION forming part of Letters Patent No. 711,572, dated October'21, 1902. 7

Application filed January 27, 1902. Serial No- 91,509. (No specimens.)

To all whom, it may concern:

Be it known that I, LEoPoLn KAHL, manufacturing chemist, a subject ofthe German Emperor,residingatSchwientochlowitz,Prussia, Germany, haveinvented a new and useful Oxalic-Acid Ester of Paracresol and Process ofMaking Same, of which the following is a specification.

Coal-tar, and consequently also the mixture of crude phenols obtainedfrom it, contains, as is well known, the three isomericcresolsortho,n1eta, and para cresol-the Xylenols,and similar substancesin addition to the phenol. The phenol and orthocresol may be recoveredfrom this mixture by repeated fractional distillation; but hitherto ithas not been found possible to separate by simple fractionation the paraand meta cresol, both boiling at 200 centigrade. In View of theincreasing commercial importance of the pure meta and para cresol forthe manufacture of trinitrometacresol, pure cresotinic acids, and forother purposes it is desirable, however, to possess a simple method ofseparating or obtaining the two cresols in a pure condition.

The present invention is based on the discovery that under certainconditions the paracresol will yield an oxalic-acid ester, while underthe same conditions the metacresol takes little or no part in theformation of esters, and also on the fact that oxalic-acid esters ofparacresol are insoluble in the cooled mixture.

p The details of procedure are as follows: An anhydrous oresol mixture,such as may be obtained in commerce, is brought to the temperature ofthe water-bath, about onetenth of its weight of dehydrated oxalic acidis stirred into the mixture, and the heating is continued until theWhole of the oxalic acid has entered into solution. Instead of oxalicacid the corresponding quantity of dehydrated acid oxalate (such asbioxalate or tetraoxalate) may be used, in which case the heating iscontinued until the acid oxalate has been decomposed by the paracresoland neutral oxalate has thereby been precipitated, which is subsequentlyseparated from the solution by hot filtration. The solution is thenallowed to cool, and thereby the oxalic-acid ester of the paracresolcaused to crystallize out. The ester thus obtained isfiltered andpressed, then washed with benzene or other suitable solvents in order toremove the last traces of the cresol adheringto it, and finallydecomposed with water.

The paracresol oxalic-acid ester obtained as described or from pureparacresol by means of dehydrated oxalic acid or acid oxalate is acolorless" body which resists atmospheric influences fairly well and onsublimation yields fine scales or leaflets. It enters readily intochemical reaction, is very easily soluble in alcohol, ether, and glacialacetic acid, but not soluble in benzene. When heated with benzene, itundergoes a partial decomposition of its components while yielding causethe ester always contains small quantities of water, which water duringthe process of heating causes a partial saponification. The presence ofwater is also an obstacle to the analysis of the ester, the compositionof which may be most easily determined by decomposing a considerablequantity of the freshly-compared ester into its components and weighingthe latter separately. According to such an analysis the composition ofthe acid ester is represented by the formula .oH, o n

6 oooooon.

Owing to its contents of water, as mentioned above, the melting-point ofthe ester is also not sharply defined. When heated in small tubes, suchas are commonly used for ascertaining melting-points, the estercommences to change at 90 centigrade, and at 99 it con tracts to atranslucent mass. If the heating is continued to about 185 to 186that isto say, the neighborhood of the melting-point of the anhydrous oxalicacid-the turbid matter, probably consisting of oxalic acid, meltscompletely while giving ofi gas.

As mentioned above, the ester is easily saponified-by Water Whilereconstituting the paracresol and the oxalic acid. Owing to theappreciable solubility of the paracresol in concentrated solution ofoxalic acid, this saponification of the paracresol ester is preferablyaccompanied with the addition of benparacresol to benzene. This takesplace, be-

ter steam may be used for this purpose, and

the paracresol which has separated out may be driven out with steam. Theoxalic-acid solution obtained in either case is concentrated byevaporation, and the oxalic acid deposited by this operation is againused af ter being relieved of water.

The relative quantities of oxalic acid or oxalate and cresol mixture maybe varied; but those mentioned above have been found especially useful.The temperature at which the reaction is performed may also vary withinwide limits, provided that it does not exceed the temperature ofdecomposition of the oxalic acid. Supposing, for instance, that the rawmaterial is a cresol mixture which has been relieved as far as possibleof phenol,

orthocresol, and the xylenols by distillation and which contains fortyper cent. of paracresol and sixty per cent. of metacresol, it cannot berelieved of the whole of its paracresol by a single operation accordingto the above process, because the quantity of oxalic acid that can beused at one time for the production of esters is limited by thesolubility of the oxalic-acid ester of paracresol in the cresol mixtureand depends also on the quantity of water produced during the formationof esters. This quantity should not exceed a certain limit; otherwise itwill not combine with the excess of cresol (which during the reactionserves to abstract water) sufficiently for avoiding the saponifyingeifect on the newly-formed ester. If, however, the water produced by thereaction is distilled off in a vacuum during the production of theester, the said restriction is avoided,and a greater quantity of oxalicacid may be used at one time. The poorer cresol mixture produced byfiltering and pressing the ester is completely relieved of water byheating or redistillation and is again treated with oxalic acid in themanner described above. This process is repeated until the wholequantity of paracresol has been separated. The metacresol will be foundin the residue. If the esterification of the paracresol contained in thecresol mixture is effected by means of acid oxalate, it is not necessaryto distil off the water of reaction in a Vacuum, because thesimultaneously-formed neutral oxalates are strongly hygroscopic when ina nascent state and absorb the water of crystallization while formingaqueous salts, which separate out in the shape of crystals. Theesterification of the paracresol may be performed on a crude cresolmixture still containing orthocresol and xylenol. In this case themetacresol may be subsequently recovered by repeatedfractionaldistillation of the cresol mixture relieved of paracresol.

tVhat I claim is- 1. The process for the separation of para cresol froma commercial mixture containing para and meta cresol, which consists inadding to the hot mixture sufficient anhydrous oxalic acid to transformthe paracresol into an oxalic-acid ester, allowing the said ester tocrystallize out of the solution, and separating it mechanically from thesupernatant liquid, substantially as described.

2. The process for the separation of paracresol from a commercialmixture of para and meta cresol which consists in converting theparacresol into an oxalic-acid ester by the addition of anhydrous oxalicacid to the hot mixture of cresols, allowing the said ester tocrystallize out of the mixture, separating the said ester from thesupernatant liquid, and then decomposing it by means of water,substantially as described.

3. As a new product of manufacture, oxalicacid ester of paracresolobtainable from paracresol and oxalic acid,and constituting a colorlesssolid, which is easily soluble in alcohol, ether and glacial aceticacid, insoluble in benzene, and capable of sublimation in the shape ofscales and leaflets, substantally as described.

In testimony that I claim the foregoing as my invention I have signed myname in presence of two subscribing witnesses.

LEOPOLD KAHL.

Witnesses:

FRIEDRICH RUSSIG, J OSEF SCI-IOTZ.

